DO you have a dana 80 full float? I have that, and if you have one where there is a BIG nut in the center, I just went by feel. Before I took it off, I felt how much play was in the axle by push pull meathod. Then did the nut thing untill i duplicated the feel. There is a keeper that holds the nut in place. it just taps in. you have to pull it off to adjust the nut.
Look in my readers rigs under brake job and see a pic of my axle and see if that is the same as yours
Eric